1. Field of the Invention
The present invention relates to an anthracene derivative. In addition, the present invention relates to a light-emitting material, a material for a light-emitting element, a composition for coating, light-emitting element, a light-emitting device, and an electronic device each of which uses the anthracene derivative.
2. Description of the Related Art
A display device using a light-emitting element in which an organic compound is used as a light-emitting substance (an organic EL element) has been developed rapidly as a next generation display device because it has advantages such as thinness, lightness in weight, high response speed, and low power consumption. Although there have been various obstacles, technique has been improved as far as organic EL televisions have become commercially available recently.
In an organic EL element, when voltage is applied between a pair of electrodes which interpose a light-emitting layer containing a light-emitting organic compound, electrons and holes are injected from the electrodes and are recombined to form an excited state, and when the excited state returns to a ground state, light is emitted. A wavelength of light emitted from a light-emitting substance is peculiar to the light-emitting substance; thus, by using different types of organic compounds as light-emitting substances, light-emitting elements which exhibit various wavelengths, i.e., various colors can be obtained.
In the case of a display device which is expected to display images, such as a display, at least three colors of light, i.e., red, green, and blue are required in order to reproduce full-color images. To achieve this, for example, there are following methods: a method in which a light-emitting element emitting light with a light-emitting spectrum in a wide wavelength and a color filter are combined, a method in which a light-emitting element emitting light with a shorter wavelength than the wavelength of a desired color and a color conversion layer are combined, a method in which a light-emitting element emitting light with a desired wavelength is used. Among those three methods, the final one, i.e., a method in which a desired wavelength is obtained directly is preferable because loss in energy is small if the method is used.
This method is adapted to the organic EL televisions which have become commercially available; however, in addition to that method, a color filter is used in practice, and a micro cavity structure is employed for a light-emitting element in order to improve color purity. Organic EL televisions have got many advantages but are naturally expected to provide high quality images as next generation televisions, and light-emitting elements exhibiting an appropriate emission color are required to live up to the expectation.
Light emitted from a light-emitting substance is peculiar to the substance as described above. There are many measures to improve the color purity of an organic EL television, which means that a light-emitting element which exhibits light emission of a favorable color and also satisfies other important requirements of lifetime, power consumption, and the like is very difficult to obtain. In addition, important characteristics of a light-emitting element, such as a lifetime or power consumption, do not always depend on only a substance exhibiting light emission. The characteristics are greatly affected also by layers other than a light-emitting layer, an element structure, a relationship between a light-emitting substance and a host, or the like. Therefore, there is no doubt that many kinds of materials for light-emitting elements are needed for the growth in this field. Accordingly, materials having various molecular structures for light-emitting elements have been proposed (For example, see Patent Document 1: Japanese Published Patent Application No. 2003-146951).